A lead frame on which is disposed a semiconductor chip is made of a comparatively thick material so as to have superior heat dissipation. On the other hand, an outer lead portion is made of a comparatively thin material so as to have superior molding performance. Because the outer lead supports the lead frame in process steps of manufacturing a semiconductor chip and a part of the outer lead is used as outer terminals for the semiconductor chip.
Utilizing a plurality of materials, each of the materials having different thickness, in the fabrication process steps presents increasing a number of the process steps and higher process cost. Therefore, the lead frame and the outer lead are individually formed, and the lead frame and the outer lead are subsequently coupled.
As shown in FIG. 9A, a lead frame 66 is arranged inside an outer lead 60 in process steps of manufacturing a semiconductor chip. In this process steps, coupling portions 63, 64 of the outer lead 60 and coupling acceptance portions 68, 69 of the lead frame 66 are mutually coupled. FIG. 9A also shows sending holes 61a, a frame portion 61, outer portions 62, terminal extension portions 65, and a chip mounting portion 67.
FIGS. 9B, C are cross-sectional views showing a coupling shape along the Y-Y direction in FIG. 9A. As shown in FIG. 9B, a coupling portion 64 is coupled with a coupling acceptance portion 69 by welding so as to form a welding portion 70. For another example, Japanese Patent Publication (Kokai) No. 2002-141453 discloses that a coupling portion 64a is coupled with a coupling acceptance portion 69a by caulking so as to form a caulking portion 71 as shown in FIG. 9C.
Welding or caulking can comparatively firmly couple between the outer lead 60 and the lead frame 66. On the other hand, the semiconductor chip is disposed on the chip mounting portion 67 of the lead frame 66 in process steps of manufacturing semiconductor device. The semiconductor chip and outer terminals 62 are connected by wire bonding, and are sealed by a mold resin. Subsequently, a terminal extension portion 65 and the coupling portions 63, 64 are cut off.
Stress generated by welding or caulking may cause mechanical damage in the lead frame 66 in a cutting step of a coupling portion. Therefore, a yield in fabrication steps of the semiconductor device may be decreased.
Using the welding tool or the caulking tool in the coupling steps presents comparatively longer process steps. Moreover, a fabrication cost is increased by investment in facilities.